1. Field of the Invention
This invention relates to an improved variable bore ram packer for a ram-type blowout preventer used in oil and gas drilling operations. Ram-type blowout preventers are part of a pressure control system used in oil and gas drilling operations to control unexpected well bore pressure spikes or "kicks" as they are commonly referred to in the industry.
The blowout preventer has a body with a vertical bore and a pair of laterally disposed opposing bonnet assemblies. Each bonnet assembly includes a piston which is laterally moveable within the bonnet assembly by pressurized hydraulic fluid. Replaceable sealing elements called "packers" are mounted on the ends of the pistons which extend into the blowout preventer bore. When these pistons are moved to a closed position, commonly referred to as "closing the blowout preventer" or "closing the rams", the vertical bore of the blowout preventer is sealed and the "kick" is contained. These "packers" are available in a variety of configurations designed to seal the blowout preventer bore when the opposing pistons are moved to their closed position. One type of packer has ends designed to seal around pipe of a specific size in the blowout preventer bore when the blowout preventer is "closed." Other rams are configured to seal around a range of pipe sizes. It is the type designed to seal around a range of pipe sizes, called variable bore ram packers to which the present invention is directed.
The ram packers form a pressure tight seal during a kick until the well bore pressure can be controlled. The well bore pressure can reach several thousand pounds per square inch during a "kick." Each ram packer has a semicircular opening in its front face to form a seal around 180.degree. of the outer periphery of the pipe. When the rams are closed as described above, the opposing ram packers meet and seal the entire 360.degree. periphery of the pipe.
Additionally, the variable bore ram packer is required to seal against the drill pipe during a "stripping" operation. During a stripping operation, the drill pipe is pulled from the well bore with the blowout preventer closed against the drill pipe. This results in enormous wear and tear on the ram packer, particularly the elastomeric sealing element. In an effort to minimize the tearing and loss of mass of the elastomeric sealing element, numerous modifications and additions to the ram packer and particularly the elastomeric sealing element in ram-type blowout preventers have been used. Problems associated with these modifications and additions to the variable bore ram packers include excessive loss of mass of the elastomeric seal element, expensive to manufacture and maintain and requiring special oversized blowout preventer rams to accept the variable bore ram packers. The variable bore ram packer of the current invention offers a substantial improvement by offering a simple, easy to manufacture variable bore ram packer which accommodates a range of pipe sizes, minimizes wear and tear of the elastomeric seal element and is useable in standard size blowout preventer rams.
2. Description of Related Art
Various types of variable bore ram packer designs have been shown and used.
U.S. Pat. No. 3,915,424 to R. K. LeRouax shows an early version of a variable bore ram packer. This apparatus utilizes a plurality of annular segments which use interlocking edges and shoulders to form anti-extrusion members. These anti-extrusion members allow radial and circumferential movement of the elastomeric sealing element to which they are bonded. As the elastomeric sealing element moves to seal around different size tubular members, the anti-extrusion members move also to conform to the diameter of the tubular member and reduce extrusion of the elastomeric sealing element. U.S. Pat. Nos. 3,915,425 and 3,915,426 to R. K. LeRouax and U.S. Pat. No. 4,444,404 to G. C. Parks, Jr., apply this same technology again by varying the shape and method of interlocking the anti-extrusion members.
U.S. Pat. No. 4,229,012 to B. C. Williams, III, discloses another type of variable bore packer for a ram type blowout preventer utilizing irising elements embedded in the elastomeric sealing element to operate like a camera shutter. The irising elements include triangular shaped upper and lower plates connected by a rib. The irising elements are designed and positioned within the elastomeric sealing element to support the sealing element as it closes on different sized tubular members. A similar concept is shown in U.S. Pat. No. 4,332,367 to N. A. Nelson in which the anti-extrusion elements are tapered rectangularly shaped upper and lower plates connected by a rib which are designed to move radially and reduce sealing element extrusion.
As variable bore ram packers seal against different size tubular members, the elastomeric sealing element undergoes considerable deformation which can lead to tearing and severe damage to the elastomeric sealing element. Various patents have disclosed the use of voids or recesses in the elastomeric sealing element to minimize damage. Chief among these are U.S. Pat. No.4,265,424 to M. R. Jones, U.S. Pat. No. 4,456,215 to T. R. Bishop et al., U.S. Pat. No.4,461,448 to W. Huey et al. and U.S. Pat. No. 4,550,895 to D. U. Shaffer.
Another consideration in the design of variable bore ram packers is whether the elastomeric sealing element should be flush with the front edge of packer or extending slightly outwardly. Examples of variable ram packers with the elastomeric sealing element extending outwardly are shown in U.S. Pat. No. 4,647,002 to M. K. Crutchfield and U.S. Pat. No. 5,127,623 to G. L. McDugle. These configurations do not lend themselves to long packer life.
A final group of variable bore ram packers utilizes a series of arcuate segments stacked vertically, with a set of arcuate segments for each of the pipe sizes to be sealed against. U.S. Pat. Nos. 5,005,802 and 5,294,088 to D. J. McWhorter et al. typify these designs. While these designs seal well on different sized tubular members, the stacking of the arcuate segments requires the use of a special blowout preventer ram to accommodate the additional height.